An Interfacial Engineering Approach of Flower-like Li⁺ Preintercalated Co–Cu Phosphate for Solid-State Hybrid Energy Storage Device

Despite recent interest in Li-ion hybrid supercapacitors (Li-HSCs) with a cathode (pseudocapacitive-type) and an anode (capacitor-type), the inherently poor electrical conductivity and structural instability of the cathode limit the practical applications of Li-HSCs. Preintercalating alkali metal ions in the crystal structure is beneficial to boost structural stability, accelerate charge transfer, and enhance electrochemical performance. Accordingly, we developed a self-supported Li+ preintercalated Co–Cu phosphate nano/microarchitecture on nickel foam (NF) via a facile hydrothermal method. Interestingly, preintercalating Li+ ions into the Co–Cu phosphate tunnels enhanced the number of active sites, electronic conductivity, and diffusion of Li+ ions in the bulk electrodes. Additionally, owing to the in situ development of Li+ preintercalated Co–Cu phosphate, the Li-CoCuP4 electrode exhibited a remarkable specific capacity of 368 mAh/g (1326 C/g, 4.75 F/cm) at a 1.0 A/g current density with notable long-term stability. Generally, lithium-based electrolytes exhibit higher energy densities than potassium-based electrolytes. Consequently, the Li-CoCuP4//PVA-LiClO4//rGO solid-state hybrid supercapacitor (SSHS) yielded a high capacity of 156 mAh/g (561 C/g) and a superb energy density of 124.85 Wh/kg at a power density of 0.75 kW/kg and a current density of 1.0 A/g. Furthermore, after 5000 cycles, it maintained a robust cycling lifespan of 94%, manifesting its practical feasibility. This work provides a new prototype for Li+ ion-based energy storage devices and validates that the preintercalation of Li+ ions is an effective strategy to enhance the electrochemical efficiency of layered microstructured Co–Cu phosphate materials.